scholarly journals Longitudinal biases in the Seychelles Dome simulated by 35 ocean-atmosphere coupled general circulation models

2013 ◽  
Vol 118 (2) ◽  
pp. 831-846 ◽  
Author(s):  
Motoki Nagura ◽  
Wataru Sasaki ◽  
Tomoki Tozuka ◽  
Jing-Jia Luo ◽  
Swadhin K. Behera ◽  
...  
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Ocean Atmosphere ◽  
Coupled General Circulation Models

Why is the AMOC Monostable in Coupled General Circulation Models?

2014 ◽  
Vol 27 (6) ◽  
pp. 2427-2443 ◽  
Author(s):  
Wei Liu ◽  
Zhengyu Liu ◽  
Esther C. Brady
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Meridional Overturning Circulation ◽  
Surface Salinity ◽  
Sensitivity Experiment ◽  
Climate System Model ◽  
Control Simulation ◽  
Coupled General Circulation Models ◽  
The Stability ◽  
Flux Adjustment

Abstract This paper is concerned with the question: why do coupled general circulation models (CGCM) seem to be biased toward a monostable Atlantic meridional overturning circulation (AMOC)? In particular, the authors investigate whether the monostable behavior of the CGCMs is caused by a bias of model surface climatology. First observational literature is reviewed, and it is suggested that the AMOC is likely to be bistable in the real world in the past and present. Then the stability of the AMOC in the NCAR Community Climate System Model, version 3 (CCSM3) is studied by comparing the present-day control simulation (without flux adjustment) with a sensitivity experiment with flux adjustment. It is found that the monostable AMOC in the control simulation is altered to a bistable AMOC in the flux-adjustment experiment because a reduction of the surface salinity biases in the tropical and northern North Atlantic leads to a reduction of the bias of freshwater transport in the Atlantic. In particular, the tropical bias associated with the double ITCZ reduces salinity in the upper South Atlantic Ocean and, in turn, the AMOC freshwater export, which tends to overstabilize the AMOC and therefore biases the AMOC from bistable toward monostable state. This conclusion is consistent with a further analysis of the stability indicator of two groups of IPCC Fourth Assessment Report (AR4) CGCMs: one without and the other with flux adjustment. Because the tropical bias is a common feature among all CGCMs without flux adjustment, the authors propose that the surface climate bias, notably the tropical bias in the Atlantic, may contribute significantly to the monostability of AMOC behavior in current CGCMs.

Global coupled ocean-atmosphere general circulation models in LASG/IAP

2004 ◽  
Vol 21 (3) ◽  
pp. 444-455 ◽  
Author(s):  
Yu Yongqiang ◽  
Zhang Xuehong ◽  
Guo Yufu
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Ocean Atmosphere

Status and Improvements of Coupled General Circulation Models

Science ◽  
2000 ◽  
Vol 288 (5473) ◽  
pp. 1991-1997 ◽  
Author(s):  
H. Grassl
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Coupled General Circulation Models

The Double-ITCZ Syndrome in Coupled General Circulation Models: The Role of Large-Scale Vertical Circulation Regimes

2010 ◽  
Vol 23 (5) ◽  
pp. 1127-1145 ◽  
Author(s):  
A. Bellucci ◽  
S. Gualdi ◽  
A. Navarra
Keyword(s):  
Surface Temperature ◽  
Systematic Error ◽  
General Circulation ◽  
Large Scale ◽  
Deep Convection ◽  
General Circulation Models ◽  
Intertropical Convergence Zone ◽  
Convergence Zone ◽  
Vertical Circulation ◽  
Coupled General Circulation Models

Abstract The double–intertropical convergence zone (DI) systematic error, affecting state-of-the-art coupled general circulation models (CGCMs), is examined in the multimodel Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) ensemble of simulations of the twentieth-century climate. The aim of this study is to quantify the DI error on precipitation in the tropical Pacific, with a specific focus on the relationship between the DI error and the representation of large-scale vertical circulation regimes in climate models. The DI rainfall signal is analyzed using a regime-sorting approach for the vertical circulation regimes. Through the use of this compositing technique, precipitation events are regime sorted based on the large-scale vertical motions, as represented by the midtropospheric Lagrangian pressure tendency ω500 dynamical proxy. This methodology allows partition of the precipitation signal into deep and shallow convective components. Following the regime-sorting diagnosis, the total DI bias is split into an error affecting the magnitude of precipitation associated with individual convective events and an error affecting the frequency of occurrence of single convective regimes. It is shown that, despite the existing large intramodel differences, CGCMs can be ultimately grouped into a few homogenous clusters, each featuring a well-defined rainfall–vertical circulation relationship in the DI region. Three major behavioral clusters are identified within the AR4 models ensemble: two unimodal distributions, featuring maximum precipitation under subsidence and deep convection regimes, respectively, and one bimodal distribution, displaying both components. Extending this analysis to both coupled and uncoupled (atmosphere only) AR4 simulations reveals that the DI bias in CGCMs is mainly due to the overly frequent occurrence of deep convection regimes, whereas the error on rainfall magnitude associated with individual convective events is overall consistent with errors already present in the corresponding atmosphere stand-alone simulations. A critical parameter controlling the strength of the DI systematic error is identified in the model-dependent sea surface temperature (SST) threshold leading to the onset of deep convection (THR), combined with the average SST in the southeastern Pacific. The models featuring a THR that is systematically colder (warmer) than their mean surface temperature are more (less) prone to exhibit a spurious southern intertropical convergence zone.

scholarly journals Ocean mixed layer processes in the Pacific Decadal Oscillation in coupled general circulation models

2012 ◽  
Vol 41 (5-6) ◽  
pp. 1407-1417 ◽  
Author(s):  
Bo Young Yim ◽  
Yign Noh ◽  
Sang-Wook Yeh ◽  
Jong-Seong Kug ◽  
Hong Sik Min ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Pacific Decadal Oscillation ◽  
General Circulation ◽  
General Circulation Models ◽  
Ocean Mixed Layer ◽  
The Pacific ◽  
Coupled General Circulation Models

Investigating quasi-resonant Rossby waves with an idealized general circulation model

2020 ◽  
Author(s):  
Todd Mooring ◽  
Marianna Linz
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Rossby Waves ◽  
Circulation Model ◽  
General Circulation Models ◽  
Weather Extremes ◽  
Dynamical Mechanism ◽  
Atmospheric Physics ◽  
Coupled General Circulation Models ◽  
Mean State

<p>Petoukhov et al.’s (2013, PNAS) hypothesis of quasi-resonant Rossby waves as a mechanism for destructive weather extremes—both heat- and rain-related, observed and projected—has received a great deal of attention in recent years.  Most notably, it has been used for diagnostic studies of reanalysis products and full-physics atmospheric or coupled general circulation models. However, studies of this sort essentially assume (rather than test) the validity of the underlying theory.</p><p>Since the quasi-resonance theoretical arguments do not explicitly involve the full complexity of atmospheric physics, it ought to be possible to test them within the much simpler framework of an idealized general circulation model. By carefully constructing the forcing fields for such a model, we will achieve control of its zonal mean state and thus the waveguide properties of the zonal jet. We will explore the properties of the quasi-stationary Rossby waves in such simulations to test whether they have the properties predicted by Petoukhov et al. By testing this dynamical mechanism in a simplified model, we can better understand its applicability and limitations for investigations of future climate.</p>

scholarly journals Understanding El Niño in Ocean–Atmosphere General Circulation Models: Progress and Challenges

2009 ◽  
Vol 90 (3) ◽  
pp. 325-340 ◽  
Author(s):  
Eric Guilyardi ◽  
Andrew Wittenberg ◽  
Alexey Fedorov ◽  
Mat Collins ◽  
Chunzai Wang ◽  
...  
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
General Circulation Models ◽  
Ocean Atmosphere

scholarly journals Are 100 ensemble members enough to capture the remote atmospheric response to +2°C Arctic sea ice loss ?

2021 ◽  
pp. 1-54
Author(s):  
Y. Peings ◽  
Z. Labe ◽  
G. Magnusdottir
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Internal Variability ◽  
General Circulation Models ◽  
Arctic Sea Ice ◽  
Model Assessment ◽  
Atmospheric Response ◽  
Arctic Sea ◽  
Ocean Atmosphere ◽  
Arctic Sea Ice Loss

AbstractThis study presents results from the Polar Amplification Multimodel Intercomparison Project (PAMIP) single-year time-slice experiments that aim to isolate the atmospheric response to Arctic sea ice loss at global warming levels of +2°C. Using two General Circulation Models (GCMs), the ensemble size is increased up to 300 ensemble members, beyond the recommended 100 members. After partitioning the response in groups of 100-ensemble members, the reproducibility of the results is evaluated, with a focus on the response of the mid-latitude jet streams in the North Atlantic and North Pacific. Both atmosphere-only and coupled ocean-atmosphere PAMIP experiments are analyzed. Substantial differences in the mid-latitude response are found among the different experiment subsets, suggesting that 100-member ensembles are still significantly influenced by internal variability, which can mislead conclusions. Despite an overall stronger response, the coupled ocean-atmosphere runs exhibit greater spread due to additional ENSO-related internal variability when the ocean is interactive. The lack of consistency in the response is true for anomalies that are statistically significant according to Student’s-t and False Discovery Rate tests. This is problematic for the multi-model assessment of the response, as some of the spread may be attributed to different model sensitivities while it is due to internal variability. We propose a method to overcome this consistency issue, that allows for more robust conclusions when only 100 ensemble members are used.

Sign in / Sign up

Export Citation Format

Share Document